1. Field of the Invention:
This invention relates to the art of rotatable electrical connectors for use with flexible electric cables, and particularly for use with coiled cords that are widely used today on telephone receivers for connecting the handset to the telephone base. One of the advantages of coiled telephone cords is that they are able to stretch for convenient use, while they retract into a compact length when not in use. This rotatable connector of the present invention is mainly for use with lightweight, light-duty telephone cords rather than high voltage, high current electrical cable systems.
2. Description of the Prior Art:
A thorough search of the prior art was made, and no patents were found relating to rotatable electrical connectors for coiled telephone cords. Most, if not all, of the prior art described heavy-duty commercial or industrial electrical connectors, which will now be described.
The Mohr U.S. Pat. No. 3,195,094 relates to an electric cable coupling comprising mutually concentric, rotatable units that are capable of transmitting electrical current therethrough. Each electrical circuit has an internal ring member surrounded by a plurality of cylindrical rollers which are confined by an external ring member, and this unit is held together by split rings or helical springs. This design appears to have an excessive amount of friction to restrain an easy turning action between the movable parts.
The Norwegian Pat. No. 106,382, issued in 1965, appears to be derived from the above-cited Mohr patent, or vice versa.
The German Pat. No. 1,152,459 describes a cable connector with mutually concentric and rotatable parts for polyphase current in which a series of ball bearings is provided inside an insulating housing. These ball bearings are under spring pressure, and they carry the electrical current. An internal tube is provided which holds a compact bundle of conductors that reach inside the insulating housing. The number of conductors corresponds to the number of electrical phases.
The Wendell et al U.S. Pat. No. 3,599,165 describes an electrical coupling device providing a series of continuous, unbroken, unsliding electrical connections between two relatively rotatable members over a limited angular displacement. There is a spiral strip connector that is made of thin material having a relatively low spring constant that is capable of cyclic operation for a sufficient large number of rotative displacements as desired without excessive fatigue and rupture.
The Hayward et al U.S. Pat. No. 3,847,463 describes a cable connector for electrically connecting a coaxial cable to a fixed device, such as a coupler or amplifier, for use in a cable antenna television system CATV which is adapted to accommodate drop leads to individual subscribers' television sets.
The Charles et al U.S. Pat. No. 3,972,577 describes rotating electrical contacts in a device that is intended to be used on apparatus submerged underwater at great depth where it would be subjected to a high hydrostatic pressure. One example of such a device would be a rotary antenna of panoramic sonars intended to operate at great depth. This device also must be watertight. This patent uses mercury or an alloy of gallium and indium as the conductive liquid.
The British Pat. No. 331,997 describes swivel connections for electric cables using ball bearing rings. One metal ring has spring wipe contacts that are adapted to press lightly on the face of the opposite ring and provide continuous electric contact therebetween. Apparently, the ball race is not an electrical conductor. There is a ball and socket joint between the spindle of one member and the spindle of the opposite member.